A great variety of apparatus is currently in use in which various operations are performed by the application of external force, e.g., by a user's finger, to obtain optical or electrical contact between two adjacent, closely spaced apart flexible layers to generate signals which are generally processed further by an external electrical circuit. Examples of these include elevator floor selection buttons, certain computer terminals, and, lately, touch sensitive overlay screens that permit the user of a computer monitor to manipulate records stored within the computer.
When a touch sensitive overlay (TSO) assembly is utilized with a computer monitor, in a manner that requires that light be transmitted through multiple transparent layers so that the user may manipulate data stored within the computer, it has become increasingly important that spacing apart of adjacent optically transparent, and sometimes also electrically conductive, layers within the TSO assembly be achieved by optically non-intrusive means. One approach is to provide small plastic non-conductive bumps or points, as best seen in FIGS. 1 and 2, between adjacent pressure-sensitive electrically conductive layers to separate them. Such plastic spacer bumps are usually distributed in a uniform manner and are visible, and therefore are intrusive to the user. An example of such an approach is found in U. S. Pat. No. 4,423,299, issued to Gurol et al in 1983, for a "Touch Sensitive Transparent Switch Array".
As an even more general proposition, even for light-opaque adjacent closely spaced layers, e.g., a touch sensitive key-board face lighted from the user's side, it may be very desirable to ensure either electrically conductive or non-conductive separation in a predetermined manner.
A need, therefore, exists for a simple, inexpensive solution to the problem of separating two normally parallel layers by a predetermined distance without eliminating the facility for an external force to cause the surfaces to move closer to each other to thereby obtain a positionally determinable contact between them. When the layers to be separated are electrically conductive, the separation between them must be provided electrically non-conductively.